Photoflash lamp

ABSTRACT

A percussive-type photoflash lamp having a primer comprising a wire anvil partially coated with two or more discrete layers of fulminating material having different compositions and coaxially supported within a tube in a manner providing a clearance between the coating of fulminating material and the inner wall of the tube. The inner layer of fulminating material comprises a known mixture of red phosphorus, a powdered combustible metal, and an oxidizer; however, the outer layer contains substantially less or no red phosphorus.

United States Patent [1 1 1] 3,840,325 Shaffer Oct. 8, 1974 PHOTOFLASH LAMP Primary Examiner-Carroll Dority, Jr. [75] lnventor: John W. Shaffer, Williamsport, Pa. Attorney Agent or firm-Edward Coleman [73] Assignee: GTE Sylvania Incorporated,

Danvers, Mass. [57] ABSTRACT [22] Filed; Oct 29, 1973 A percussive-type photoflash lamp having a primer comprising a wire anvil partially coated with two or PP N05 410,382 more discrete layers of fulminating material having different compositions and coaxially supported within 52 us. Cl. 431/93 3 tube in a manner Providing a elear'anee between the 51 Int. Cl. F2lk 5/02 eeating of fulminating material and the inner Wall of 58 Field of Search 431/93 the tube The inner layer of fulminating materiel prises a known mixture of red phosphorus, a pow- [56] References Cited dered combustible metal, and an oxidizer; however, UNITED STATES PATENTS the outer layer contains substantially less or no red phosphorus. 3,667,992 6/1972 Brown et al. 431/93 X 12 Claims, 3 Drawing Figures i 28 V it? 3'4 g/ I23 .7] 5i? 1/ l 2 2/ 5 1, l 3 5:,

I 1? 5 'i'; 21 g k as shredded zirconium foil,

1 PHOTOFLASH LAMP BACKGROUND OF THE INVENTION This invention relates to the manufacture of photoflash lamps and more particularly those of the percussive type. Generally speaking, a percussive-type photoflash lamp comprises an hermetically sealed, lighttransmitting envelope containing a source of actinic light and having a primer secured thereto. More particularly, the percussive-type photoflash lamp may comprise a length of glass tubing constricted to a tip at one end thereof and having a primer sealed therein at the other end thereof. The length of glass tubing which defines the lamp envelope contains a combustible, such and a combustionsupporting gas, such as oxygen. The primer may comprise a metal tube and a charge of fulminating material on a wire anvil supported therein. A deflector bead is disposed on the wire anvil just above the primer tube to deflect and control the ejection of hot particles of fulminating material therefrom. Operation of the percussive-type photoflash lamp is initiated by an impact onto the tube to cause deflagration of the fulminating material up through the tube to ignite the combustible disposed in the lamp envelope.

The requirements that must be met by a fulminating material for percussive flashlamps are unique and differ appreciably from those for flashlamps used heretofore in which a paste of fulminating material is heated by the passage of electric current through a wire filament until ignition occurs. Energy input to the paste usually extends over a period of one or more milliseconds. In contrast, energy input to the fulminating material of a percussive flashlamp is in the form of a single nearly-instantaneous impact, the duration of which would be measured in microseconds. Unless ignition occurs during this single momentary event, the lamp has failed. Accordingly, the fulminating material for percussive flashlamps must be much more sensitive than is the ignition paste for filament-ignited lamps.

The fulminating material for percussive flashlamps comprises four major ingredients: an oxidizer in the form of a chlorate salt, generally potassium or sodium chlorate; a fuel, such as red phosphorus, that ignites by friction or impact in the presence of the oxidizer; a binding agent, such as hydroxyethyl cellulose, to adhere the fulminating material to a specified location in the flashlamp; and a combustible metal powder, such as titanium, for attenuating the reaction between the phosphorus and oxidizer, and transporting combustion from the fulminating material to the shredded metallic combustible in the lamp.

Early percussive lamp manufacturing processes employed a primer dip pot which contained a complete mixture of all of the fulminating material ingredients in a paint like slurry preferably using an aqueous vehicle. The method of preparing this fulminating material paste comprised: (l) blending all ingredients, except the chlorate, with some water to provide as part A an aqueous slurry or solution containing the phosphorus and titanium, etc.; (2) preparing as part B an aqueous slurry or solution of the chlorate; and (3) mixing the phosphate and chlorate slurries together. The aqueous slurry of red phosphorus, etc. and the oxidizer slurry were stored separately and, in the interest of safety, were blended together just before use. Either of the components is relatively safe, even when dry; but when combined and dried, the resultant material burns on impact or abrasion.

A safer, so called absorbed oxidizer technique was later developed and is described in US. Pat. No. 3,667,992. According to this process, an oxidizer-free part A composition is applied to the anvil and dried. The coating is then permeated with sodium-chlorate by dipping into an aqueous solution containing from 10% to 52% sodium chlorate by weight.,As the concentrated solution of sodium chlorate penetrates the red phos-- phorus containing coating, a degree of intimacy comparable to that obtained with completely mixed waterbased fulminating material is realized. In this manner the hazardous fulminating material is formed in place of the anvil in milligram quantities.

Potassium chlorate has very limited solubility in water and, thus, is unsuited to the absorbed oxidizer process. Even complete mix fulminating materials using potassium chlorate are characterized by the presence of discrete crystals of the oxidizer dispersed through the dried coating. Because of their heterogeneous nature such fulminating materials are of limited reliability at low impact energy and burn less rapidly than do more homogeneous materials. Another characteristics of aqueous complete-mix fulminating materials using potassium chlorate as the oxidizer is the tendency toward growth of the larger oxidizer crystals at the expense of the finer ones present. The required spacing of the anvil and primer tube issuch that large crystals may contact the inner surface of the tube and promote inadvertent lamp ignition upon being subjected to movement or vibration. See US. Pat. No. 3,735,679.

The use of more soluble chlorates, 'such as sodium chlorate, results in a more homogeneous dried coating of fulminating material. The reliability at low impact energy is higher thereby providing a margin of safety between energy required for operation and the energy delivered by even age-weakened firing springs. The burning rate of these more homogeneous compositions is somewhat faster.

Certain camera models recently introduced to the market have shutter timing characteristics which are quite critical with respect to the timing characteristics of the light output from-percussive flashlamps. In particular, the rise time of the light output tends to be too fast, with the associated possibility of photographic underexposure with those lamps that are somewhat faster than average. In effect, part of the light output is generated before the camera shutter is sufficiently open to make use of that light.

The timing characteristics of flashlamps are conveniently described in terms of three numbers: rise time,

peak time, and decay time. FIG. 1 shows the light output-time relationship of percussive flashlamps. The solid curve, labeled X, represents the typical output curve of lamps using a homogeneous fulminating material of the sodium chlorate type. The dashed curve, Y, is a representative output curve of lamps using the inventive principles to be described hereinafter. The lamp peak time is the time in milliseconds at which the lamp attains peak intensity. The rise and decay times are those times when the lamp output curve respectively intersects a given output intensity, in this case 10,000 zonal lumens.

Lamp rise time can be increased (delayed) by lowering the deflection bead on the anvil so as to increase its throttling effect on the fulminating material discharge. However, resultant bead interception of burning metal particles from the fulminating material seriously reduces the reliability of igniting the shredded combustible within the lamp. This effect is particularly pronounced when, for example, the combustible has been moved upward in the vessel away from the opening of the primer tube. Such shred movement may occur due to handling and shipping of the lamps.

Another means of extending rise time is to use less soluble oxidizers, such as potassium chlorate, so as to effect heterogeneous compositions. This, however, precludes use of the safer absorbed oxidizer process.

The rise time may also be extended by use of less oxidizer or by use of high weight ratios of metal powder to red phosphorus. Either of these changes results in greatly reduced impact sensitivity and reliability.

The weight of fulminating material used per lamp can be reduced to effect a slower output timing characteristic. The reliability of shred ignition falls off rapdily below about 0.5 milligrams so that this approach is not acceptable for a commercial product.

SUMMARY OF THE INVENTION In view of the foregoing it is an object of this invention to provide a percussive photoflash lamp that is safe to manufacture and that has the delayed timing characteristics required for certain camera models.

Another object is to provide a percussive flashlamp that simultaneously has high reliability at low impact energy and slower output timing characteristics.

These and other objects, advantages and features are attained, in accordance with the principles of this invention, by using a plurality of discrete layers of fulminating material, each having a different composition, in place of the previous single composition body of fulminating material on the primer anvil. The innermost layer of fulminating material comprises a fuel, an oxidizer, a combustible metal powder, and a binder; whereas the outermost layer of fulminating material comprises an oxidizer, a binder and a combustible metal powder in a proportion greater than the proportion of metal powder in the innermost layer. The fuel is typically red phosphorus, and the outermost layer may also contain red phosphorus, in a proportion less than the proportion of red phosphorus in the inner most layer. The oxidizer preferably comprises a highly water soluble chlorate suitable for the aforementioned absorbed oxidizer application method.

BRIEF DESCRIPTION OF THE DMWINGS The invention will be more fully described hereinafter in conjunction with the accompanying drawings in which:

FIG. 1, to which previous reference has been made, shows comparative curves of light output vs. time for two percussive flashlamps, one employing a conventional charge of fulminating material and the other employing two discrete layers of different fulminating compositions in accordance with the invention;

FIG. 2 is an elevational view partly in section of a percussive type photoflash lamp; and

FIG. 3 is a greatly enlarged fragmentary cross-section of the primer tube of the lamp of FIG. 2 illustrating the layered structure of fulminating material in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENT The percussive-type photoflash lamp illustrated in FIG. 1 comprises a length of glass tubing defining an hermetically sealed lamp envelope 2 constricted at one end to define an exhaust tip 4 and shaped to define a seal 6 about aprimer 8 at the other end thereof. The primer 8 comprises a metal tube 10 and a wire anvil l2 coated with a charge of fulminating material 14. A combustible such as filamentary zirconium l6 and a combustion-supporting gas such as oxygen are disposed within the lamp envelope. The wire anvil 12 is centered within the tube 10 and held in place by a crimp 18 just above the head 20 of the anvil. Additional means, such as lobes 22 on wire anvil 12, are also used to aid in stabilizing and supporting it substantially coaxial within the primer tube 10 and insuring clearance between the fulminating material 14 and the inside wall of the tube 10. A metal or glass bead 24, attached to the wire anvil 12 just above the inner mouth of the primer tube 10, eliminates burnthroughs and functions as a deflector to deflect and control the ejection of hot particles of fulminating material from the primer tube.

I have found that extended lamp rise times and high reliability can both be achieved, along with retention of the safety advantages of the absorbed oxidizer application method, by use of two or more different layers to form the body of fulminating material 14. The structure of such a primer arrangement is illustrated in section in FIG. 3. The inner most layer 26 is initially applied as an oxidizer-free part A similar in composition to the above discussed prior art part A mixtures containing red phosphorus. After drying of layer 26, a second oxidizer free layer 28 (in this case the outermost layer), which contains substantially less or no red phosphorus, is applied over layer 26. After drying of layer 28, the anvil is immersed in a soluble oxidizer solution such as sodium chlorate, and redried. In this manner, an impact sensitive body of fulminating material 14 comprising two distinct layers 26 and 28 of different compositions is safely formed.

By way of specific example, a prior art fulminating material used in lamps associated with light output curve X in FIG. 1 had the following dried part A composition by weight; 72.33% titanium powder; 24.08% red phosphorus; 1.44% hydroxyethyl cellulose as a binder; 1.18% sodium lignin sulfonate as a chemical dispersing agent; 0.21% sodium octyl sulfate as a wetting agent; 0.08% N-(3-chloroallyl) hexaminium chloride as a bactericide; 0.64% magnesium oxide for maintaining the mixture slightly alkaline; and 0.04% sulfur for improving shelf life and impact sensitivity. This dried coating was then dipped into an aqueous solution containing 25% by weight of dissolved sodium chlorate and redried. The total weight of this prior art, single composition body of fulminating material was held between about 0.5 and 1.0 milligram per lamp by adjustment of the water content in the part A slurry.

The two-layer body of fulminating material 14, used in lamps associated with curve Y in FIG. 1, contains two different compositions. In this specific embodiment of the invention, the innermost layer 26, exclusive of oxidizer, has a dried composition identical to the part A formula given in the preceding paragraph. The outermost layer 28, however, contains a much larger proportion of combustible metal powder than the proportion of metal powder in the innermost layer 26. More specifically, the composition of layer 28, exclusive of oxidizer, contains 96.41% by weight titanium powder and no red phosphorus. The percentages of all other ingredients is the same as that given in the preceding paragraph. After application and drying, consecutively, of coatings 26 and 28, the anvil 12 is immersed into a 25% by weight aqueous solution of sodium chlorate, which permeates both layers. When dried, both of the layers 26 and 28 contain the necessary oxidizer component, sodium chlorate, to provide an impact-sensitive body of fulminating material. The total weight of the two layers of dried fulminating material is from about 0.5 to 1.0 milligram.

Referring to FIG. 1, the following test data represents the average photometric timing characteristics measured for a first group of prior art lamps containing a single composition fulminating material as described hereinbefore (curve X) and a second group of lamps containing the above-described two-layer body of fulminating material according to the invention (curve Y), the two groups of lamps differing only in the fulminating material:

This data is presented solely to illustrate the behavior attainable by the principles taught herein.

The innermost part A layer 26, exclusive of oxidizer, should comprise red phosphorus to the extent of at least by weight on a dried basis. Lesser amounts would give unsatisfactory reliability, whereas concentrations greater than about 79% by weight result in excessive burning violence. Along with the red phosphorus, layer 26 should include from 1% to 5% of a water soluble binding agent, such as hydroxyethyl cellulose, and from to 89% by weight of a combustible metal powder such as zirconium, titanium, boron, titanium hydride, or zirconium hydride, or combinations thereof. Use of the several additional minor ingredients and their concentrations is optional and is not essential to the inventive principles related herein.

The outermost layer 28, exclusive of oxidizer, should comprise principally a powdered combustible metal, for example from the group mentioned above, from 51% to about 99.5% by dried weight. A binding agent is needed in the proportion of 0.5% to about 5% by weight. A nonmetallic fuel, such as red phosphorus, may be present from about 1% to 48.5% if desired. However, the presence of red phosphorus in the outer layer will at least partially negate the low inadvertent ignition characteristic that is expected with phosphorus-free outer layers. The amount of red phosphorus can also be used to control the delay in rise and peak time; e.g. a lower percentage will slow rise time, whereas a larger percentage of red phosphorus in the outer layer will increase rise time. Here again, the inclusion of the minor ingredients is optional and does not contribute to operation of the inventive principles related herein.

After drying of both oxidizer-free layers the coating is imbibed with a soluble chlorate salt solution such as sodium chlorate. The concentration of the oxidizer solution may be from about 10% to 52% by weight depending on the solubility of the salt chosen. We prefer a concentration of 25%. Total dried weight of the twolayer fulminating material should be held between 0.5 to 1.0 milligram per lamp. The relative dry weights of layers 26 and 28 may be respectively varied from about 4:1 (for faster rise time) to about 1:4 (for slower rise time) by adjustment of the water contents of the two respective slurries. I prefer a nominal 1:1 ratio for ease of application (i.e., each layer is from 0.25 to 0.5 milligram).

A further advantage of the fulminating material principles taught herein is a greatly attenuated discharge velocity from the primer tube. This reduction in gas flow helps to prevent compaction and/or movement of the shredded combustible in the lamp with attendant loss is shred combustion efficiency and light output.

Yet another advantage results when the outermost layer 28 is devoid of phosphorus. Such a phosphorusfree outer layer is not as sensitive to unintentional ignition resulting from lateral wall scuffing, as opposed to an indenting impact. Accordingly, this embodiment of the invention significantly reduces the fraction of lamps that flash inadvertently due to vibration.

Other chlorate salts which have cations not catalytically reactive toward red phosphorus and which are soluble to the extent of 15% or greater by"weight in water at 20C may be used; for example, calcium chlorate, lithium chlorate, magnesium chlorate, aluminum chlorate, and zinc chlorate. However, the extreme deliquescenceof these materials may render their use'in flashlamps more difficult with regard to drying and maintaining the coating dry prior'to hermetic closure of the flashlamp. Similarly, phosphorus s'esquisulfide may be used in place of red phosphorus, if desired, al-

though a slight loss in sensitivity may be noted. Also, alternate metal powders such as, for example, hafnium, thorium, cerium, or the rare earths etc., could be used in the fulminating material.

A third or additional layers of alternate compositions (e.g. less reactive first and third coatings sandwiching a more reactive second intermediate layer) could be used, but render the process tedious and difi'rcult to control in a high speed production operation. The degree of fulminating material attenuation attainable by the principles related herein may permit manufacture of percussive flashlamps having no deflector beads on the anvils thereof.

Accordingly, although the invention has been described with respect to a specific embodiment, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the spirit and scope of the invention.

What I claim is:

l. A photoflash lamp comprising:

an hermetically sealed, light-transmitting envelope;

a quantity of filamentary combustible material located within said envelope;

a combustion-supporting gas in said envelope;

and a primer secured to and extending from one end of said envelope and in communication therewith, said primer including a tube sealed in said end of said envelope and having an exposed segment outside said envelope, a wire anvil located substan-- tially coaxial within said tube, and a body of fulminating material located on said wire anvil intermediate its ends and on that segment of said wire anvil located in said exposed segment of said tube but spaced from the inside wall thereof, said body of fulminating material comprising a plurality of discrete layers each having a different composition;

the innermost layer of said fulminating material adjacent said wire anvil comprising a fuel, an oxidizer, a combustible metal powder and a binder;

and the outermost layer of said fulminating material comprising an oxidizer, a binder, and a combustible metal powder in a proportion greater than the proportion of metal powder in said innermost layer.

2. The lamp of claim 1 wherein said oxidizer in said layers of fulminating material is a chlorate having a water solubility of greater than by weight at C and having a cation not catalytically reactive toward said fuel.

3. The lamp of claim 1 wherein the combustible metal powder in said layers of fulminating material comprises either zirconium, titanium, boron, titanium hydride, or zirconium hydride, or a combination thereof.

4. The lamp of claim phorus.

5. The lamp of claim 4 wherein said outermost layer of fulminating material further contains red phosphorus in a proportion less than the proportion of red phosphorus in said innermost layer.

6. The lamp of claim 4 wherein the dried composition by weight of said innermost layer of fulminating mate- 1 wherein said fuel is red phosrial exclusive of said oxidizer comprises from about 10% to 79% red phosphorus, from about 20% to 89% combustible metal powder, and from about 1% to 5% water soluble binding agent;

and wherein the dried composition by weight of said outermost layer of fulminating material exclusive of said oxidizer comprises from about 1% to 48.5% red phosphorus, from about 51% to 99.5% combustible metal powder, and from about 0.5% to 5% water soluble binding agent.

7. The lamp of claim 4 wherein said oxidizer in said layers of fulminating material is a chlorate having a water solubility of greater thant 15% by weight at 20C and having a cation not catalytically reactive toward said fuel.

8. The lamp of claim 7 wherein said oxidizer is sodium chlorate.

9. The lamp of claim 8 wherein the combustible metal powder in said layers of fulminating material comprises either zirconium, titanium, boron, titanium hydride, or zirconium hydride, or a combination thereof.

10. The lamp of claim 9 wherein said binder in said layers of fulminating material comprises hydroxyethyl cellulose, and the compositions of said inner and outermost layers of fulminating material further include relatively small quantities of magnesium oxide, sulfur, sodium lignin sulfonate, sodium octyl sulfate andN-(3- chloroallyl) hexaminium chloride.

11. The lamp of claim 7 wherein the compositions of said inner and outermost layers of fulminating material further include relatively small quantities of a chemical dispersing agent, a wetting agent, a bactericide, sulfur, and magnesium oxide. v

12. The. lamp of claim 4 wherein said bodyof fulminating material comprises two discrete layers of fulminating material having different compositions. 

1. A photoflash lamp comprising: an hermetically sealed, light-transmitting envelope; a quantity of filamentary combustible material located within said envelope; a combustion-supporting gas in said envelope; and a primer secured to and extending from one end of said envelope and in communication therewith, said primer including a tube sealed in said end of said envelope and having an exposed segment outside said envelope, a wire anvil located substantially coaxial within said tube, and a body of fulminating material located on said wire anvil intermediate its ends and on that segment of said wire anvil located in said exposed segment of said tube but spaced from the inside wall thereof, said body of fulminating material comprising a plurality of discrete layers each having a different composition; the innermost layer of said fulminating material adjacent said wire anvil comprising a fuel, an oxidizer, a combustible metal powder and a binder; and the outermost layer of said fulminating material comprising an oxidizer, a binder, and a combustible metal powder in a proportion greater than the proportion of metal powder in said innermost layer.
 2. The lamp of claim 1 wherein said oxidizer in said layers of fulminating material is a chlorate having a water solubility of greater than 15% by weight at 20*C and having a cation not catalytically reactive toward said fuel.
 3. The lamp of claim 1 wherein the combustible metal powder in said layers of fulminating material comprises either zirconium, titanium, boron, titanium hydride, or zirconium hydride, or a combination thereof.
 4. The lamp of claim 1 wherein said fuel is red phosphorus.
 5. The lamp of claim 4 wherein said outermost layer of fulminating material further contains red phosphorus in a proportion less than the proportion of red phosphorus in said innermost layer.
 6. The lamp of claim 4 wherein the dried composition by weight of said innermost layer of fulminating material exclusive of said oxidizer comprises from about 10% to 79% red phosphorus, from about 20% to 89% combustible metal powder, and from about 1% to 5% water soluble binding agent; and wherein the dried composition by weight of said outermost layer of fulminating material exclusive of said oxidizer comprises from about 1% to 48.5% red phosphorus, from about 51% to 99.5% combustible metal powder, and from about 0.5% to 5% water soluble binding agent.
 7. The lamp of claim 4 wherein said oxidizer in said layers of fulminating material is a chlorate having a water solubility of greater thant 15% by weight at 20*C and having a cation not catalytically reactive toward said fuel.
 8. The lamp of claim 7 wherein said oxidizer is sodium chlorate.
 9. The lamp of claim 8 wherein the combustible metal powder in said layers of fulminating Material comprises either zirconium, titanium, boron, titanium hydride, or zirconium hydride, or a combination thereof.
 10. The lamp of claim 9 wherein said binder in said layers of fulminating material comprises hydroxyethyl cellulose, and the compositions of said inner and outermost layers of fulminating material further include relatively small quantities of magnesium oxide, sulfur, sodium lignin sulfonate, sodium octyl sulfate and N-(3-chloroallyl) hexaminium chloride.
 11. The lamp of claim 7 wherein the compositions of said inner and outermost layers of fulminating material further include relatively small quantities of a chemical dispersing agent, a wetting agent, a bactericide, sulfur, and magnesium oxide.
 12. The lamp of claim 4 wherein said body of fulminating material comprises two discrete layers of fulminating material having different compositions. 